The present invention relates to an apparatus for suppressing warping of an optical disk during its rotary driving, and an optical disk apparatus equipped with such an apparatus for suppressing warping.
FIG. 1 is a perspective view showing a constitution of an essential part of a conventional magnetic field modulation type optical disk apparatus. In the drawing, numeral 53 denotes a carriage that is approximately L-shaped in lateral side view. Numerals 41, 41 denote guide shafts to guide the carriage 53. The carriage 53 is formed of: (1) a carriage body 54 of rectangular parallelepiped which is long in the radial direction of a donut shaped optical disk 2 (which is driven in rotation by a rotary spindle) 1; and (2) a supporting part 55 which is located at the end part of the outer peripheral side (front side) of the optical disk 2, where this supporting part extends upright of the carriage body 54. A load arm 61, to be described later, is fixed to the upper end of the supporting part 55.
The guide shafts 41, 41 are provided on one side of the optical disk 2 at a predetermined distance in parallel with each other so that the center line between the two guide shafts 41, 41 is in the radial direction of the optical disk 2. The carriage body 54 is provided with two through-holes having approximately the same diameters as those of the guide shafts 41, 41, the through-holes penetrating through the carriage body 54 from its front to the back side (the inner peripheral side of the optical disk 2) in parallel with each other at a predetermined distance. By letting the guide shafts 41, 41 through the through-holes, the carriage 53 is swingably supported in the radial direction of the optical disk 2.
At the central lower part in front of the carriage body 54 there is provided a light conductive hole 56 for leading light beam B in parallel with the through-hole so as to allow the light beam B from a fixed light source disposed opposite to the light conductive hole 56 to be incident in the light conductive hole 56. On the back side of the carriage body 54 there is provided an opening communicating with the light conductive hole 56, and a lens holder 81 is held in cantilever at an end of the front side of the opening. The lens holder 81 has a rectangular tubular shape which has opening vertically and is longer in the thickness direction of the carriage body 54 when viewed from the side. On the upper and lower faces of the end of the front side of the opening there are fixed the base parts of the flat springs 84 having the U-shaped notches, respectively, and the apexes of the flat springs 84 are fixed to the upper and lower faces of the lens holder 81 on the front side.
On the front side in the lens holder 81, an objective lens 82 is fixed in parallel with the upper face of the carriage body 54. The objective lens 82 condenses the light beam B that is reflected upwardly by a reflecting mirror disposed opposite below the objective lens 82 and emits it to the optical disk 2. The lens holder 81 is inserted at the back side of a leg of the U-shaped yoke 85 for focusing, which is fixed to the carriage body 54. On the inner face of the other leg of the yoke 85 for focusing, a magnet 86 for focusing is fitted. Also, around the lens holder 81 a focus coil 83 is fitted which is wound multiple times around a shaft parallel with the optical axis of the objective lens 82. The focus coil 83 is disposed orthogonal with a magnetic field formed by the magnet 86 for focusing and the yoke 85 for focusing. And, by leading electric current in the focus coil 83, focus control is made to cause ascending or descending of the lens holder 81 which holds the objective lens 82, and on which the focus coil 83 is wound, in the direction of the optical axis of the objective lens 82.
The load arm 61 fixed to the upper end of the supporting part 55 is a flat spring, which extends from the upper end of the supporting part 55 toward the optical disk 2 by a predetermined size in parallel with the carriage body 54, and from that place the load arm 61 is inclined toward the optical disk 2 at a predetermined angle of inclination. The tip of the load arm 61 is acute, and is situated at the predetermined position above the lens holder 81. Also, the tip is made to be movable up and down by a lift device. To the tip of the load arm 61 there is fitted, in a swingable manner, a slider 71 having a rectangular shape in plan view so that the optical disk 2 is set between the slider 71 and the lens holder 81. To the lower face of the slider 71 there is fixed a magnetic head 70 made by winding a coil around a core so as to be positioned at the center of the objective lens 82. The slider 71 is in direct contact with the surface of the optical disk 2 when the optical disk 2 is in a still state.
By the air current generated by the rotary driving of the optical disk 2, buoyancy is generated on the slider 71, but as a force directed toward the optical disk 2 is exerted to the slider 71 side by the spring force of the load arm 61, the slider 71 floats at the position where the two items are balanced. The buoyancy as described above is strong when the distance between the slider 71 and the optical disk 2 is short, and weak when the distance is long. On the other hand, the force to be exerted to the slider 71 from the load arm 61 is weak when the distance between the slider 71 and the optical disk 2 is short, and strong when the distance is long. Accordingly, during the rotation of the optical disk 2, the distance between the slider 71 and the optical disk 2 is kept constant.
On the back side portions of both sides of the carriage body 54 there are fixed tubular drive coils 44, 44 wound in multiple turns around a shaft in parallel with the guide shafts 41, 41. Also, on both sides of the carriage body 54, there are disposed the frame shaped yokes 42, 42 which are open up and down and long in the lengthwise direction of the guide shafts 41, 41 in a manner that the lateral surfaces in the longitudinal direction of the two yokes 42, 42 and the lateral surfaces of the carriage body 54 are in parallel with one another. On the respective side walls opposite to the carriage body 54 of the two yokes 42, 42, the drive coils 44, 44 are externally accommodated without contact. On the inner surface of the other side walls respectively of the two yokes 42, 42, there are fitted plate form magnets 43, 43 having approximately the same length as those of the yokes 42, 42, so that a magnetic field formed by the magnets 43, 43 and yokes 42, 42 crosses at a right angle with parts of the drive coils 44, 44.
When the reciprocal current is led to the drive coils 44, 44, by the reciprocal actions with the magnetic field, the carriage 53 supporting the drive coils 44, 44 advances or recedes in the lengthwise direction of the yokes 42, 42, i.e., in the radial direction of the optical disk 2. By this step, there is performed an access control to converge the light beam B to be irradiated on the optical disk 2 from the objective lens 82 on the upper surface of the optical disk 2 and move its spot to the required track of the optical disk 2, and a track control to have the spot of the light beam B follow the track of access. Alternatively, the track control can be realized by providing an actuator for moving the lens holder 81 to the radial direction of the optical disk 2. At this time, the magnetic head 70 is always positioned at the center of the objective lens 82 because it is supported to the carriage 53 by the load arm 61 to which the slider 71 fixed with the magnetic head 70 is fixed.
And, while irradiating the light beam B of predetermined intensity on the recording face of the optical disk 2 while carrying out the controls as described above, a magnetic field in one of reciprocal directions is applied from the magnetic head 70 opposed to the objective lens 82, by which the required data are written in the optical disk 2. To the recording face of the optical disk 2 in which the data are written, the light beam B is irradiated without applying the magnetic field, and the direction of rotation on a deflection face of the reflection light from the optical disk 2 is detected, by which the data written in the optical disk 2 is read out.
In such an apparatus, the spot diameter of the light beam must be reduced by enlarging the numerical aperture of the objective lens and the recording density of the data must be improved. In this case, as the numerical aperture of the objective lens is made larger, due to the warping or slight inclination of the optical disk, aberration of the light beam becomes large, and the detection precision of the reflected light in the direction of rotation is lowered. For this reason, there is proposed an optical disk whose thickness is reduced to about half that (0.6 mm) of a conventional disk. By this step, it is schemed that the aberration of the light beam B which is incident from the lower face of the optical disk 2 and converges on the upper face side caused by inclination or warping of optical disk is decreased to improve the recording density.
By the way, when, as described above, the slider to which the magnetic head is fixed is disposed opposite to the optical disk, downward force is exerted to the optical disk by the counter-action of buoyancy formed on the slider, i.e., by the air current whose direction is changed to the direction toward the optical disk by the slider. When using an optical disk of conventional thickness, the optical disk is not affected by this force, but when using a thin optical disk, there is a problem that warping is formed on the optical disk by a force, and large aberration of the light beam is produced by this warping. Further, if the magnetic head is fixed to the sliding type slider which is in contact with the optical disk in place of the floating type slider as mentioned above, the optical disk shows warping. On the other hand, in the case of using the thin optical disk, this warping occurs slightly even by its own weight, and therefore, even in the optical disk apparatuses other than the magnetic field modulation type, there are problems similar to the above.